In-situ mass-electrochemical study of surface redox potential and interfacial chemical reactions of Li(Na)FePO4 nanocrystals for Li(Na)-ion batteries. (July 2017)

• Record Type: Journal Article
• Authors: Song, Xiaohe; Liu, Tongchao; Amine, Joseph; Duan, Yandong; Zheng, Jiaxin; Lin, Yuan; Pan, Feng
• Is Part Of: Nano energy. Volume 37(2017:Jul.)
• Page Start: 90
• Page End: 97
• Publication Date: 2017-07
• Subjects: Lithium ion battery -- Surface redox potential -- Electrochemical quartz crystal microbalance -- Density functional theory -- Interfacial structure; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2017.05.019
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: In this work, an in-situ experimental mass-electrochemical investigation of the LiFePO4 (LFP) and NaFePO4 (NFP)electrolyte interfacial chemical reactions and surface redox potential is achieved by adopting electrochemical quartz crystal microbalance (EQCM) to monitor the mass change trend. In organic electrolyte, LFP (NFP) cathode's mass decreases/increases during the charge/discharge process because of deintercalation/intercalation of Li (Na) ions, which is an normal phenomenon which is generally known. However, the mass-potential curve for LFP nanocrystals in aqueous electrolyte show an anomalous mass change interval (AMCI) around 3.42 V (vs. Li/Li + ) where the cathode's mass increase in the charging process and mass decrease in the discharging process, which doesn't obey the normal law of mass change. Through density functional theory (DFT) calculations, we gain a microscopic picture of the solid-liquid interface structure with a reconstructed LFP (010)/H2 O and NFP (010)/H2 O interface. Taken together, it's concluded that the surface redox potential of LFP is around 3.31 V, which is lower than the bulk potential (3.42 V) and the desolvation/solvation rate of surficial Li-ion is lower than the bulk Li-ion diffusion rate. While for NFP, it's surface redox potential is almost the same as the bulk one. Graphical abstract: Highlights: EQCM is applied to study the Li(Na)FePO4 /electrolyte interfacial reactions and surface redox potential. The mass-potential curve for LiFePO4 in aqueous electrolyte shows an anomalous mass change interval around 3.42 V (vs. Li/Li + ). DFT study presents a microscopic picture of the LFP/H2 O, NFP/H2 O interface structures and surface redox potentials. The electrochemical process of LFP/H2 O interface is obtained by combining experimental and DFT study.